People in the UK have been urged to stay at least 2m, or six-and-a-half feet, away from anyone who they don't live with, to avoid catching or spreading COVID-19.
But the distance may be a non-scientific estimate that just caught on in countries around the world, as top researchers say there is not solid evidence to back it up.
Other nations have cut their rules down to a 1m gap, which advocates say could help businesses get back to work faster and help to kick-start the economy.
Shops could fit more customers in if the rule was 1m, not 2m, and there would also be more scope for hospitality businesses to return to a semblance of normality without huge gaps between tables and chairs.
Professor Robert Dingwall, a sociologist at Nottingham Trent University and a member of government advisory group NERVTAG (New and Emerging Respiratory Virus Threats Advisory Group) made the 'fragile evidence' comments this morning.
He said that the World Health Organization and other countries in Europe had reduced this distance to one metre but the UK is persisting with the full 2m.
Professor Dingwall said on BBC Radio 4: 'The World Health Organization recommends a one metre distance, Denmark has adopted it since the beginning of last week.
'If you probe around the recommendations of distance in Europe you will find that a lot of countries have also gone for this really on the basis of a better understanding of the scientific evidence around the possible transmission of infection.'
Iain Duncan-Smith, a former Conservative Party Cabinet minister has also called for the rule to be relaxed, saying it will be impossible to maintain in pubs and restaurants.
Professor Dingwall has spoken out about the weakness of the two-metre rule in the past, suggesting it could safely be cut at least to 1.5m.
He has even suggested that it is being clung to by British officials because they don't feel they can trust the public to manage a shorter distance.
Speaking to The Telegraph earlier this month Professor Dingwall said: 'There is a fair degree of consensus now among people who are more expert on these things than I am that outdoor transmission is negligible...
'Personally I think we could quite safely go to 1.5metres, which seems to be an internationally acceptable standard, inside and outside.'
He added that officials had told him they 'did not think the British population would understand what one metre was and we could not trust them to observe it so we doubled it to be on the safe side'.
And in further comments made to Radio 4 in April, Professor Dingwall said it would be harder to enforce rules without scientific evidence.
'I think it will be much harder to get compliance with some of the measures that really do not have an evidence base,' he said. 'I mean the two-metre rule was conjured up out of nowhere.'
He referred to it as a 'rule of thumb' rather than a scientifically proven measure.
Although the British Government has loosened some of its lockdown restrictions, such as allowing people to spend as much time outside as they want to, everyone is still required to stick to the social distancing rule.
Lines on supermarket floors to keep shoppers apart, spaced out queues outside shops and takeaways and walking in the road to get round people on then pavement are now commonplace.
The thinking behind the rule is that it dramatically reduces the risk of virus droplets being able to jump between people.
The coronavirus spreads on invisible droplets of fluid that are expelled from someone's mouth and nose when they breathe out, cough or sneeze.
If someone else breathes them in they will catch the infection when the virus latches on to cells in their airways.
Over the space of two metres the vast majority of these particles drop to the floor, away from potential victims, scientists say.
Former Conservative Party leader, Iain Duncan-Smith, has also urged the government to drop its two-metre rule so hospitality staff can return to work.
Opening shops, restaurants and pubs would be fraught with difficulties if everyone had to be 2m apart, limiting the amount of customers that could be in a place and keeping profits low.
He said on Radio 4's Today programme yesterday: 'We're the only country certainly in Europe that I know of [that uses the two-metre rule]...
'I think when it comes to the hospitality sector, I think we do need to look at it very carefully.
'So we do need to look at how they manage that process and give them some flexibility.'
The cautious two-metre rule is actually used in Switzerland, the US, Spain and Italy, as well as in the UK.
While detractors say it is an unnecessarily large distance, experts suggest that the risk of catching the virus is considerably higher at one metre than it is at two.
Andrew Curran, chief scientific adviser at the Health and Safety Executive said being exposed to someone for 'a few seconds' at a one metre distance could equate to around an hour of being two metres away from the same person, the Sunday Telegraph reported.
He said: 'If the exposure at a distance of less than two metres is going to be for a short period of time, you manage the risk in the context of duration and orientation.
'There is some physics in this and the Sage sub-group is looking at that to provide better information.
'For example, if you were exposed for a few seconds at one metre, that is about the same as being exposed for a longer period of time - an hour, say - at two metres. It is that order of magnitude.
'There may be elements within a job where there is exposure for a short period, but where the risk is so low it can be managed.'
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